Crankshaft bearing arrangement of a combustion engine

ABSTRACT

The present disclosure refers to a crankshaft bearing arrangement for an internal combustion engine. The bearing arrangement comprises: a bearing arranged at a crankshaft of an internal combustion engine; a bearing seat for housing the bearing; and a sealing arrangement for sealing against the crankshaft and the bearing seat. The at least one part of the bearing seat has a reinforcement arranged in the bearing seat, and a surface of the at least one part of the bearing seat, which surface bears against the bearing, is made from a plastic material.

TECHNICAL FIELD

The present disclosure relates to a crankshaft bearing arrangement of acombustion engine, and, more specifically, to a crankshaft bearingarrangement of an internal combustion engine of a hand-held motor-driventool.

BACKGROUND

In the development of combustion engines for motor-driven tools, such aschainsaws, hedge trimmers, grass trimmers etc., bearing sleeves havebeen used to eliminate the need for after-treatment of bearing seats ofcrankshaft bearings after the bearings seats have been manufactured.

In U.S. Pat. No. 4,974,973 and WO97/45649, crankshaft bearingarrangements have been described using such bearing sleeves. In thebearing arrangement of, for example, U.S. Pat. No. 4,974,973, a bearingcan be arranged in a bearing sleeve, which is formed as a tin cup with arubber coated outer periphery. The rubber coated outer periphery isarranged to compensate for tolerances, e.g. size variations in theproduction of bearing seats and to seal against the cylinder and thecrankcase. Also, the arrangement has an internal periphery provided witha sealing ring to seal against the crankshaft.

Even if such arrangements have a lot of advantages, some exemplaryproblems may occur as follows:

-   -   Due to the rather large tolerances in such an arrangement, there        is a risk that the bearing is either too loosely arranged in the        sleeve, with a result that the bearing may rotate in the bearing        sleeve or that the bearing including the bearing sleeve will        rotate in the bearing seat, or that the bearing will press too        hard in the sleeve, risking obliqueness of the bearing or that        the bearing and/or the bearing sleeve is squeezed in the bearing        seat such that the bearing and/or the bearing sleeve finally        breaks.    -   Even if dimensions are achieved for which a proper squeezing of        the bearing and the bearing sleeve is achieved, it may be        difficult to seal such an arrangement. As a result, it may be        necessary to seal during operation with a substantial amount of        silicone glue between the bearing seat and bearing sleeve.

Also, such a solution is rather expensive to produce, since an expensivekind of rubber is usually used for the rubber-coated outer periphery.

SUMMARY

An object of the present disclosure is to create an improved crankshaftbearing arrangement which solves the above-mentioned problems.

This is solved by a crankshaft bearing arrangement disclosed herein.

According to a first embodiment, a crankshaft bearing arrangement isarranged such that at least one part of the bearing seat has areinforcement arranged in the bearing seat, and a surface of the atleast one part of the bearing seat, which bears against the bearing, ismade of a plastic material. The bearing arrangement also has a sealingarrangement for sealing against the crankshaft and bearing seat.

By having such a reinforcement, it would be possible to use a plasticmaterial for the surface of the bearing seat without risking acompression set in the plastic material. Another advantage compared tothe prior art solutions using a tin cup as a bearing sleeve, is thatsuch a bearing sleeve can be omitted in this solution, resulting insmaller tolerances between bearing seat and bearing, i.e., manufacturingsize variations. Still, existing construction tolerances can be receivedby the nature of the plastic material. Also, the plastic material can beproduced without after-treatment with a low tolerance compared to, e.g.,a metallic material. Therefore, with the arrangement according to theembodiment, there is low risk that the bearing is too loosely held inthe bearing seat, such that it may rotate or is too hardly held and istilted or damaged in any other way. Since the position between thebearing is well defined, a proper function of the crankshaft assemblyincluding piston rod, and good cooperation of crankshaft assembly andcylinder is ensured, which will result in good engine characteristicsand low emissions.

Another advantage with this arrangement is that the diameter of thebearing arrangement can be reduced since there is no bearing sleeve,which results in a more cost-effective arrangement. Also, when there isno bearing sleeve, the arrangement will be lighter and morecost-effective.

By arranging the surface of plastic material as a layer between thebearing and the reinforcement, the arrangement will be more resistant toloads, i.e., it may be exposed to rather high loads without risking acompression set in the plastic material. This is especially true if theplastic material is a fibre-reinforced plastic material.

In some embodiments, a cost-efficient sealing arrangement can be used,which can be produced from simple rubber materials and still achieve asatisfactory sealing against bearing seats and crankshaft. Also, such asealing arrangement can be produced as one unit at the time ofmanufacture.

By arranging the sealing arrangement such that it has at least oneprotrusion arranged in a pushing engagement with the bearing, tolerancesin the axial direction of the crankshaft can be received by theprotrusions.

By arranging the at least one protrusion of the sealing arrangement suchthat it bears against an outer ring of the bearing, a displacement canbe achieved between an outer ring and an inner ring of the bearing.Therefore, when the bearing is realized as a ball bearing, it is ensuredthat the balls of the ball bearing will be in contact with both theinner and the outer ring of the bearing. Due to this measure, thebearing will achieve a long life.

By arranging a number of protrusions forming a discontinuous ringbearing against an outer ring of the bearing, the sealing arrangementwill contribute to centering the bearing in an axial direction of thecrankshaft.

By arranging the at least one protrusion with a tapered shape, acompression that is proportional to the pressure from the bearing willbe achieved. Therefore, dimension variations in an axial direction dueto manufacturing tolerances can be well received independent of the sizeof the dimension variations.

According to a second aspect of the disclosure, an internal combustionengine is provided, comprising a crankshaft and at least one arrangementaccording to any of the embodiments described in this document.

According to third aspect of the disclosure, a hand-held motor-driventool is provided, comprising an internal combustion engine having acrankshaft and at least one arrangement according to any of theembodiments described in this document.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will in the following be described in more detail withreference to the enclosed drawings, wherein:

FIG. 1 illustrates an embodiment of a crankshaft bearing arrangement ina vertical cross-sectional view in an axial plane of a crankshaft atwhich a bearing arrangement is arranged.

FIG. 2 illustrates an embodiment of a crankshaft bearing arrangement ina vertical cross-sectional view in section I-I of FIG. 1.

FIG. 3 illustrates an enlargement of a part of FIG. 1 describing a partof a sealing arrangement according to an embodiment.

FIG. 4 illustrates a schematic front view of a side of a sealingarrangement facing the bearing, according to an embodiment.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments will be described more fully hereinafter withreference to the accompanying drawings. Other embodiments arecontemplated in many different forms and this disclosure should not beconstrued as limited to the embodiments set forth herein; rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the disclosure to thoseskilled in the art. In the drawings, like numbers refer to likeelements.

In the embodiments described in the figures, a crankshaft 16 is shown,which is journalled in two bearings 10, in the form of ball bearings.Although, other types of bearings might also be used. Between the twobearings 10, and mounted on the crankshaft is a crankshaft assembly 14with piston rod and counterweights. The bearings 10 are inserted in abearing seat, which in this embodiment, comprises an upper half 15,which is a lower part of a cylinder of an internal combustion engine,and a lower half 11, which is a part of a crankcase of a tool in whichthe arrangement is installed. Each bearing is supported by the twohalves of the bearing seat in such a way that the bearing seat housesthe bearings.

The lower half 11 of the bearing seat has a reinforcement 12 arranged asa layer of metal inside the bearing seat for receiving a pressure forcefrom each bearing. The reinforcement is coated by a plastic material,which provides a surface 13 of the lower half of the bearing seat, whichbears directly against the bearing. Therefore, the surface 13 of plasticmaterial is arranged as a layer between the bearing 10 and thereinforcement layer 12. The surface 13 is of a fibre-reinforced plasticmaterial, which can endure high loads and temperatures that may occur ina held-held motor-driven tool, such as a chainsaw. The surface is madeas thin as possible for the manufacturing process. Typically, when usingan injection casting procedure, the plastic surface 13 will be 1-1.5 mm.Typically, the reinforcement layer 12 has a thickness of approximately2-6 mm, depending, for example, on the size of the engine. The surfaceof plastic material bearing against the bearing may be made of the sameplastic material as the rest of the crankcase. Therefore, thereinforcement will be embedded in the plastic material of the crankcase,and the surface of the plastic material will be arranged as a layerbetween the bearing and the reinforcement. In the embodiment describedin the figures, the lower half of the bearing seat 11 has tworeinforcements, each arranged close to each bearing 10 as a metal layerinside the bearing seat.

In the embodiments described in the figures, see e.g., FIG. 2, thecylinder rests on the upper part of the crankcase. For this reason, thecrankcase has an upper surface comprising four metal areas 17, two ateach bearing, on which the cylinder stands, called the cylinder footplane. By arranging the plastic surface layer such that it extends toalso cover the area around these four metal areas, there is no risk ofleakage at the cylinder foot plane.

The embodiments described in the figures also shows two separate sealingarrangements 20, arranged against a side of each bearing 10, which facesaway from the crankshaft assembly 14, both sealing arrangements beingarranged around the crankshaft 16. Each sealing arrangement 20 isarranged as one unit to seal against the crankshaft 16 and the bearingseat 11, 15.

The sealing arrangement 20 shown in the embodiment described in thefigures is arranged as a sealing ring having a diameter substantiallyequal to the diameter of the bearing 10.

FIG. 4 shows a side of the sealing ring which, when the sealing ring isarranged on the crankshaft, faces the bearing 10. As can be seen inFIGS. 3 and 4, the sealing ring has a number of protrusions 21 arrangedat a certain radius of the ring such that the protrusions 21 bearagainst an outer ring of the bearing 10. Due to this measure, theprotrusions 21 help to push an outer ring of the bearing 10 in an axialdirection of the crankshaft 16 towards the crankshaft assembly 14, suchthat the bearings are pushed into a proper position, which results in along life for the bearings, the crankshaft assembly and the cylinder.The protrusions 21 preferably form a discontinuous ring bearing againstthe outer ring of the bearing 10. According to other embodiments, theprotrusions might also have other forms, such as a continuous ring.

The protrusions 21 preferably have a tapered shape in a directiontowards the outer ring of the bearing. Although, the protrusions 21might have other shapes, such as squared.

In the embodiment described above, the cylinder is manufactured from ametal, which means that it has a surface of metal bearing against thebearing 10. This surface has to be after-treated after the cylinder hasbeen produced in, for example, a die casting procedure to get lowtolerances and a fine surface against the bearing. Although, a cylinderof an internal combustion engine has to be after-treated anyhow,regarding other parts of a cylinder, and to make more after-treatment ofa part that anyhow experiences after-treatment is more cost-efficientthan to start an after-treatment process of a part that does not have tobe after-treated.

In the embodiment described, only the lower half of the bearing seat hasa plastic material surface bearing against the bearing and areinforcement arranged in the bearing seat close to the surface.Although, such an arrangement might also be used for an upper part ofthe bearing seat, or for parts of the lower or upper part of the bearingseat.

In the embodiment described, the bearing seat comprises a lower half ofa cylinder and an upper half of a crankcase, which are connected at ahorizontal section. In an alternative embodiment, the crankshaftarrangements in which a bearing seat is arranged coaxially onto acrankshaft as one integral part housing one bearing. In sucharrangements, the internal combustion engine comprises two bearingseats, one first bearing seat preferably housing a first bearing and onesecond bearing seat preferably housing a second bearing, arranged insuch a way that each bearing seat supports one respective bearing.Further, in this alternative embodiment the first bearing seat isintegrated in a first crankcase half and the second bearing seat isintegrated in a second crankcase half, wherein the two crankcase halvesare connected at a vertical section to form the crankcase. For sucharrangements, the whole or part of the surface of the bearing seat maybe coated with a plastic material, and correspondingly, the whole orpart of the bearing seat may have a reinforcement arranged in thebearing seat. If the reinforcement is arranged in the whole of onebearing seat, it may be arranged as a ring of, e.g., metal, arrangedclose to the surface of plastic material. Such a ring reinforcementwould be easy to manufacture and any after-treatment of a surfacebearing against the bearing would be unnecessary.

The plastic material of the surface of the bearing seat bearing againstthe bearing is preferably any kind of reinforced plastic material, suchas a carbon fibre reinforcement, a glass fibre reinforcement or anano-composite material. The surface may be of any kind of plasticmaterial that has a high heat distortion temperature. The higher theheat distortion temperature of the material and the thinner the layer ofplastic material, the less the plastic material will be deformed.

In the drawings and specification, there have been disclosed preferredembodiments and examples, although specific terms are employed, they areused in a generic and descriptive sense only and not for the purpose oflimitation, the scope of the disclosure being set forth in the followingclaims.

The invention claimed is:
 1. A crankshaft bearing arrangement for aninternal combustion engine, said bearing arrangement comprising: abearing arranged on a crankshaft of the internal combustion engine; abearing seat for housing the bearing, the bearing seat partially formedon a cylinder of the internal combustion engine; and a sealingarrangement for sealing against the crankshaft and the bearing seat;wherein at least one part of the bearing seat has at least onereinforcement arranged in the bearing seat, and in that a surface of theat least one part of the bearing seat, which bears against the bearing,is made from a plastic material, and the at least one reinforcement isarranged close to the respective bearing; wherein the sealingarrangement is arranged around the crankshaft and against a side of thebearing, which the side faces away from a crankshaft assembly, thesealing arrangement being arranged for sealing engagement with thecrankshaft and the bearing seat; wherein the sealing arrangement has aplurality of protrusions formed on another side facing towards thecrankshaft assembly in an axial direction of the crankshaft, saidplurality of protrusions arranged in a pushing engagement with thebearing, for pushing the bearing in the axial direction of thecrankshaft; wherein the bearing seat partially formed on the cylinderincludes a portion that extends in a radially inward direction relativeto the crankshaft and terminates a distance from the crankshaft; whereinthe sealing arrangement is at least partially located between theportion that extends in the radially inward direction and the bearing;and wherein the plurality of protrusions are arranged on the sealingarrangement such that it bears against an outer ring of the bearing inthe axial direction of the crankshaft.
 2. The crankshaft bearingarrangement according to claim 1, wherein the surface made of theplastic material is arranged as a layer between the bearing and the atleast one reinforcement.
 3. The crankshaft bearing arrangement accordingto claim 1, wherein the at least one reinforcement is made of metal. 4.The crankshaft bearing arrangement according to claim 1, wherein theplastic material of the surface of the at least one part of the bearingseat is a fibre-reinforced plastic material capable of withstandingloads and temperatures that occur in the internal combustion engine of ahand-held motor-driven tool.
 5. The crankshaft bearing arrangementaccording to claim 1, wherein the bearing seat comprises a lower half,and an upper half, and wherein the at least one reinforcement isarranged in the lower half.
 6. The crankshaft bearing arrangementaccording to claim 1, wherein the bearing seat is arranged as oneintegral part housing the bearing, and wherein the at least onereinforcement is arranged in a whole of the bearing seat.
 7. Thecrankshaft bearing arrangement according to claim 1, wherein theplurality of protrusions form a discontinuous ring that bears againstthe outer ring of the bearing.
 8. An internal combustion enginecomprising the crankshaft and the at least one crankshaft bearingarrangement according to claim
 1. 9. The crankshaft bearing arrangementaccording to claim 1 wherein the crankshaft bearing arrangement is acomponent of a hand-held motor-driven tool.
 10. A crankshaft bearingarrangement for an internal combustion engine, said bearing arrangementcomprising: a bearing arranged on a crankshaft of the internalcombustion engine; a bearing seat for housing the bearing, the bearingseat partially formed on a cylinder of the internal combustion engine;and a sealing arrangement for sealing against the crankshaft and thebearing seat; wherein the sealing arrangement is arranged around thecrankshaft and against a side of the bearing, which the side faces awayfrom a crankshaft assembly, the sealing arrangement being arranged forsealing engagement with the crankshaft and the bearing seat; wherein thesealing arrangement has a plurality of protrusions formed on an oppositeside facing towards the crankshaft assembly in an axial direction of thecrankshaft; wherein the bearing seat partially formed on the cylinderincludes a portion that extends in a radially inward direction relativeto the crankshaft and terminates a distance from the crankshaft; whereinthe sealing arrangement is at least partially located between theportion that extends in the radially inward direction and the bearing;and wherein the plurality of protrusions are arranged on the sealingarrangement such that it bears against an outer ring of the bearing inthe axial direction of the crankshaft.
 11. The crankshaft bearingarrangement according to claim 10, wherein at least one part of thebearing seat has at least one reinforcement arranged in the bearingseat, and in that a surface of the at least one part of the bearingseat, which bears against the bearing, is made from a plastic material,and each of the at least one reinforcements are arranged close to therespective bearing.
 12. The crankshaft bearing arrangement according toclaim 11, wherein the bearing seat is arranged as one integral parthousing the bearing, and wherein the at least one reinforcement isarranged in a whole of the bearing seat.
 13. The crankshaft bearingarrangement according to claim 10, wherein the plurality of protrusionsform a discontinuous ring that bears against the outer ring of thebearing.
 14. An internal combustion engine comprising the crankshaft andthe at least one crankshaft bearing arrangement according to claim 10.15. A crankshaft bearing arrangement for an internal combustion engine,said bearing arrangement comprising: a bearing arranged on a crankshaftof the internal combustion engine; a bearing seat for housing thebearing, the bearing seat including an upper half and a lower half; andthe upper half of the bearing seat being formed so that it onlypartially covers the bearing; a sealing arrangement for sealing againstthe crankshaft and the bearing seat; wherein the sealing arrangement isarranged around the crankshaft and against a side of the bearing, whichthe side faces away from a crankshaft assembly, the sealing arrangementbeing arranged for sealing engagement with the crankshaft and thebearing seat; wherein the sealing arrangement covers the bearing;wherein the upper half includes a portion that extends in a radiallyinward direction relative to the crankshaft and terminates a distancefrom the crankshaft; wherein the sealing arrangement is at leastpartially located between the portion that extends in the radiallyinward direction and the bearing; and wherein a plurality of protrusionsare arranged on the sealing arrangement such that it bears against anouter ring of the bearing in an axial direction of the crankshaft. 16.The crankshaft bearing arrangement according to claim 15, wherein theplurality of protrusions are formed on an opposite side facing towardsthe crankshaft assembly in the axial direction of the crankshaft.
 17. Acrankshaft bearing arrangement for an internal combustion engine, saidbearing arrangement comprising: a bearing arranged on a crankshaft ofthe internal combustion engine; a bearing seat for housing the bearing,the bearing seat partially formed on a cylinder of the internalcombustion engine; and a sealing arrangement for sealing against thecrankshaft and the bearing seat; wherein at least one part of thebearing seat has at least one reinforcement arranged in the bearingseat, and in that a surface of the at least one part of the bearingseat, which bears against the bearing, is made from a plastic material,and the at least one reinforcement arranged is arranged close to therespective bearing; wherein the sealing arrangement is arranged aroundthe crankshaft and against a side of the bearing, which the side facesaway from a crankshaft assembly, the sealing arrangement being arrangedfor sealing engagement with the crankshaft and the bearing seat; whereinthe sealing arrangement has at least one protrusion formed on anotherside facing towards the crankshaft assembly in an axial direction of thecrankshaft, said at least one protrusion arranged in a pushingengagement with the bearing, for pushing the bearing in the axialdirection of the crankshaft; wherein the bearing seat partially formedon the cylinder includes a portion that extends in a radially inwarddirection relative to the crankshaft and terminates a distance from thecrankshaft; wherein the sealing arrangement is at least partiallylocated between the portion that extends in the radially inwarddirection and the bearing; and wherein the at least one protrusion isarranged on the sealing arrangement such that it bears against an outerring of the bearing in the axial direction of the crankshaft.